Cleaning the harddrive of any machine, be it desktop, laptop or server, before either repurposing or selling (or even scrapping), should be a basic requirement of any organisation. But there is a seemingly unrelenting stream of reported incident, some of which coming from organisations that really should know better, MI6 and military contractors for example.
Is securely wiping data from drives really that difficult? Not really.
Simply boot the system with nearly any live linux system (I use Knoppix for this kind of work), then simply use dd (discussed previously to image drives) to overwrite the drive with random data. For example:
dd if=/dev/urandom of=/dev/sda
This simple overwrites the entire physical drive, sda, with random data taken from the pseudo device /dev/urandom. For more indepth info on wiping with dd and some different options see this guide.
The downside to wiping drives in this method is the length of time involved, in recent cases I have seen a 80GB drive take a little of five hours to complete.
Disclaimer: this may not make your data completely irratrievable but it should be enough to prevent the data being obtained by the simply curious. To truely ensure irratrievable data, try this method.
Disclaimer’s Disclaimer: Server destruction should only be carried out be trained professionals, InfoSanity accepts no responsibility for loss of live, limb or eyebrow)
— Andrew Waite